What is the best/cheapest way to fly to Cairns from Sydney?

Also, if i want to spend just two days in Cairns and want to explore the Reef, any suggestions from past travelers on what tours are best.

I know this isnt exactly a UNITED question, but I know a lot of FT's have been.

Thanks for all your help. Just found a seat in United First with miles for October/November and want to start planning.